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The stack is a very common data structure used in programs.
Representation of stack may be done invarious ways in computer
memory for ex. by means of a link list or a linear array.
Implementation of array-based stack is very simple. It uses top
variable to point to the topmoststack's element in the array.
Initially the value of top is set to -1. Every time we execute
push()operation the value of top is incremented by one and writes
the pushed element to storage[top].Incase of pop() operation if the
value of top not equals to -1 then will return element storage[top]
andthe value of top will be decremented by one.
The only limitation of array based implementation of stack is
that stack capacity is limited to a certainvalue and overfilling
the stack will cause an error. Though, using the ideas from dynamic
arraysimplementation, this limitation can be easily avoided.
Algorithm of Push
Let stack[Max] is an array for implementing the stack.
TOP represents top of the stack.
1. [check for stack overflow?]
If TOP = Max , then print : overflow and exit
2. Set TOP = TOP + 1
3. Set stack[TOP] := ITEM [ insert item in new TOP position]
4. Exit
Stack Implementation
Stack implemented as an array
Algorithm of Pop1. [check for stack underflow?] If top < 0 ,
then Print : underflow and exit Else [remove the top element] Set
item := stack[TOP]2. Decrement the stack top Set TOP := TOP - 13.
Return the deleted item from the stack4. Exit
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Following is the C program code for the stack operations :
In this program code following notation is used :
Stack : name of the stack array
Maxsize : maximum size of the stack
Stacktop : top position of the stack
Val : element to be pushed
#include#define maxsize 100int stack[maxsize];int
stacktop=-1;void push(int);int pop(void);void display(void);int
main(){ int choice=0,val=0; do { printf("\n\t1.Push 2.Pop 3.Display
\n\tSelect Your Choice : "); scanf("%d",&choice);
switch(choice) { case 1: printf("\tElement to be Pushed : ");
scanf("%d",&val); push(val); break; case 2: val=pop();
if(val!=-1) printf("\tPopped Element : %d\n",val);
break;
case 3: display(); break;
- default: printf("\tWrong Choice"); break; } }while(choice-1) {
printf("\tElements are:"); while(i
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We can implement Stack using linked list as well. The dynamic
allocation of memory makes it betterchoice for implementing Stacks.
In this scenario, each stack element is composed of a data
variableand a reference (in other words, a link) to the next node
in the sequence. The push() operation simplycreates a new node by
allocating memory for it (Using malloc), and then linking it to a
linked list asthe new head. A pop() operation detach the node from
the linked list, and assigns the stack pointer tothe head of the
previous second node. It also checks whether the list is empty
before popping from it.
Following is the C program code for the stack operations
:#include#include#define maxsize 10void push();void pop();void
display();struct node{ int info; struct node *link;}*start=NULL,
*new,*temp,*p;typedef struct node N;main(){ int choice,a; do {
printf("\n\t1.Push 2.Pop 3.Display \n\tSelect Your Choice : ");
scanf("%d",&choice); switch(choice) { case 1: push();
break;
case 2: pop(); break;
case 3: display(); break;
default: printf("\nInvalid choice"); break;
Stack implemented as a Linked List
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} }while(chinfo); new->link=NULL; if(start==NULL) start=new;
else { p=start; while(p->link!=NULL) p=p->link;
p->link=new; }}
void pop(){ if(start==NULL) printf("\nStack is empty"); else
if(start->link==NULL) { printf("\nThe deleted element is :
%d",start->info); free(start); start=NULL; } else { p=start;
while(p->link!=NULL) { temp=p; p=p->link; } printf("\nDeleted
element is : %d\n", p->info); temp->link=NULL; free(p);
}}void display(){
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if(start==NULL) printf("\nStack is empty"); else { printf("\nThe
elements are : "); p=start; while(p!=NULL) {
printf("%d",p->info); p=p->link; } printf("\n"); }}
